Oh, Canada..., the true north strong and free. What is your grow zone (or first and last frost dates)? Just curious. You must be having some long days about now.
Regarding e coli - I am no expert and hold no degree in soil sciences, but my sister (who is and does) once told me that 'if you had any idea how much e coli exists in your pants, you would boil them in bleach every day". Her point was that e coli is all around us and that a healthy immune system can deal with it at normal levels under normal circumstances.
On the other hand, from what I remember about the several, serious e coli recalls of spinach, lettuce, etc. over the past decade, it was not that it was on the leaf surface (that could be washed off) but that it was within the cell structure itself (from the water source). Your 'turd hill' is in essence a two year old compost pile and should be perfectly safe. As to the 'fresh toppings' that may or may not be included, I can only say, we all place our bets. I would go with it.
You could always follow 'survival training' protocol. When trying to access the safety of a food source, you would first crush up a bit and apply it to a non-critical piece of flesh (not a joint crease). If no reaction in 24 hrs apply same to a bit of your lip. If still no reaction, chew a small piece. Then, if no reaction, eat a leaf. If still no reaction, eat moderately. After that, pig out.
In your case, you could grow some quick spinach, lettuce, bok choy, radish, whatever, and just taste a bit. Wait a day. If good, eat a little more and so on. I think the greatest risk would be to eat a full, normal serving before you were sure of its safety.
As to your MIL issues. Well, that can be more difficult. Old habits die hard (hey, I've got an idea for a movie). First lesson to learn is to not become that yourself as you progress (age). We all have our heros and villains to guide us. Be thankful, otherwise - how would we know what to be or not to be? (hey, I've got an idea for a play).
It is so great that 'turd hill' is from your own cattle, with known meds, feds and beds. I'm assuming you have a good supply (made fresh daily). Perhaps dear hubby could be careful to eliminate any fresh toppings in your future deposits. The hot center is the safest place of any compost pile.
I'm going to assume your 60 sq ft raised bed is probably 6 x 10 or there abouts. If you divided it in thirds, you could 'develop' one third, plant some short season (lettuce, spinach, radish etc.) in the next third and your long season crops in the last third. You could then later plant fall crops in the first 'developed' third, while you 'develop' the 'short season' third and then finally develop the last third in late fall. All ready to go in spring.
Regarding weeding. I would definitley use well composted manure as a mulch. In a short while, you could show MIL how few the weeds be. Then she might allow you to mulch even just a part of the old garden, just to see. After the success of your developed bed, she might come to realize that it is a beautiful thing. That's an awful lot of 'ifs, mights and maybes - but what can you lose? The two of you might end up making raised beds together in the old garden next spring.
But I would think you gotta get that pick axe out and dig deep. It would be a good investment in my opinion. Considering the quality of your manure compost, I think you can do without the vermeculite as well as the peat.
Oh, and by the way, what are your cash crops, acreage, etc.
Good luck with whatever you decide to do.